I don't know about you guys... If the MC didnt call it pure luck, I would've thought it was pure skill. Sure, the gauntlet is a cop-out...
But it takes skill and wit to recognize that the only way to beat a boss with armor is to attack the openings. And to do that, he would need to get close enough, and to do that, he would need to get the boss to drop its guard, and to do that, he would have to fake it out. That takes real game sense.